I. Field
The present disclosure relates to systems and methods for linear positioning.
II. Description of Related Art
Position sensing is widely used in a number of industrial and commercial applications, such as automotive, aviation and manufacturing. For instance, linear position sensing systems may be used in manufacturing applications for determining the relative positions of different components of manufacturing equipment. As one example, a linear positioning system could be used to determine the position of a drill bit chuck assembly relative to a fixed position on a drill press in order to control the depth of a bore in a material, such as in an application using robotic equipment. As another example, linear positioning systems may be implemented as part of cruise control systems for passenger vehicles. In such applications, a linear position sensing system may be used to determine and control throttle position when the vehicle is operating with a cruise control system activated. There are, of course, countless other applications in which position sensing systems may be employed.
Traditionally, positioning sensing systems have been contact based. In such contact-based systems, certain components of the positioning system are placed in physical contact (e.g., a metal contact, brush or the like contacting a track or groove) where a linear position is determined based on the physical point of contact between the components. However, because the components of such a system move with respect to each other, such approaches are prone to failure due to a number of factors.
For instance, debris, such as dirt, dust or other matter, may collect in a track or groove (e.g., along which a contact may travel), thus preventing an accurate determination of position due to such debris interfering with physical contact between components. Also, such contact-based systems are further prone to reliability problems due to physical wear of the components at the point (or points) of contact that results from the movement of the parts relative to one another. For instance, as those components experience physical wear, that wear will eventually result in the components no longer making physical contact at one or more points along a corresponding path of travel. This loss of contact results in such a positioning system not working as expected due to loss of signal (e.g., signal drops).
One approach that is becoming more prevalent for position sensing applications that overcomes at least some of the concerns discussed above is the use of Anisotropic Magneto-Resistive (AMR) sensors. Such solutions are non-contacting and, therefore, do not experience the reliability and wear-out concerns (due to physical contact of components) of contact-based position sensing systems discussed above. In such an approach, such as for a linear positioning system, a magnet or sensor element is affixed to a linearly moving object (such as a shaft in a piece of manufacturing equipment) and a complementary sensor or magnet is mounted in a fixed position in physical proximity to the linearly moving object.
Using such an AMR sensor, the relative direction (e.g., angle) of the resulting magnetic field from the magnet can be quantified electronically by the sensor based on a differential voltage produced by the sensor. A linear position of the magnet relative to the sensor (a linear position) may be determined based on this electrical signal, which may display a cos2 θ relationship, where θ is the angle of incidence of the magnetic field through the sensor. The principles of such approaches are described in Honeywell Application Note AN221, entitled “Applications of Magnetic Position Sensors”, which was publicly available on the Internet as of Mar. 28, 2002. Honeywell Application Note 211 (AN211) is incorporated by reference herein in its entirety.
One drawback of current approaches for linear position sensing using AMR sensors is that only a relatively small portion of the electrical signal produced by the AMR sensor is usable for position determination (e.g., approximately 50% of a “linear region” of the electrical signal when multiple sensors are used in an array). This limitation is due, in part, to the fact that such electrical signals include three “mid-point crossings” for each pass of the magnet along a given portion of a path of travel where the sensor is magnetically saturated relative to the sensor. It will be appreciated by those working in this area that the AMR sensor operating in magnetic saturation is desirable for accurate position determination.
This drawback (using only 50% of the linear region of the produced electrical signal) translates to higher cost and increased system complexity in linear positioning systems where it is desirable to determine a linear position of an object over longer distances at a given resolution. For instance, in systems where it is desirable to determine position over a linear distance that is greater than a distance corresponding with the usable portion of the electrical signal for an AMR sensor, multiple position sensors are used. The multiple sensors are arranged linearly along a path that is parallel with the path of travel with the sensor to sensor spacing being determined by the length of the section of the path of travel that corresponds with the usable portion of the electrical signal for a single sensor. It will be appreciated that in such arrangements, the sensor density is higher than would be possible if more of the linear region of the electrical signal for each sensor was usable of position determination.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.